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INA148: Common mode voltage range calculation

YOSHIHIRO KANEKO
Prodigy 40 points
Part Number: INA148
Other Parts Discussed in Thread: INA149

Tool/software:

Regarding to INA148, INA149, please share the equation to calculate common mode voltage range.

And also, could you describe common mode voltage range calculation example with below condition ?

Vs+=10V

Vs-=GND(0V)

Vref = 1.65V

In my usage, INA148 or INA149 is used for bi-directional current detection with shunt register.

There is a switch IC to change current direction. So INA148/INA149 can be located on the both high side and low side dynamically.

In high side case, V+ is 200V, power source voltage. In low side case, V+ is GND.

The amplifier output is captured by 3.3V MCU ADC. Vref is half of 3.3V. 

In my understanding, in this condition, common mode voltage range should be larger than 0-200V.

Regards

  • +1
    TI__Mastermind 22397 points

    Yoshihiro,

    The common mode is divided down by the input voltage divider connected to the non-inverting input.  So, in the case of the INA148, Vcm is Vin x Rdiv/(Rin + Rdiv) = Vin x 52.6316k / (1M + 52.6316k).  For Vin = 200V, Vcm = 10V.  The INA149 common mode works the same.  The derivation of the gain transfer function is more complex.  See PDF below for details on that:

    ina148-ina149-transfer-function.pdf

    I hope this helps!

    Best regards, Art